(a) Technical Field of the Invention
This invention is related to refractory composites containing yttria (Y2O3) which form the basis of high-density chrome materials, which in turn are mainly used as the working lining material for coal and/or petroleum coke slurry gasifiers.
(b) Description of the Prior Art
Nowadays, coal and petroleum coke slurry gasifiers are widely used. Coal slurry gasification has been conventionally regarded as an economical and efficient gasification process. Another technology has also been developed, which adopts petroleum coke as the raw material. Compared with the former, it has more advantages such as higher efficiency, more available process gas yield, and lower manufacturing costs. Cr2O3 has been adopted as the main refractory for the working lining of the two kinds of gasifiers for a long period. In early times, MgO—Cr2O3—ZrO2—SiO2 was adopted, but with the development of gas processes, the lining became easily and seriously worn and corroded, resulting in a short service life. Another new material was therefore developed, called Cr2O3—Al2O3—ZrO2 (containing more Cr2O3). This reduces the corrosion speed and prolongs the service life to some extent. However, ZrO2 will react with SiO2 and CaO. As a result, the compounds ZrO2—SiO2 and ZrO2—CaO lead to a bulking effect in the bricks and some cracks on the segments during the operation process owing to their low density and in spite of their high melting point. Under temperature stress and mechanical stress, those cracks are gradually widened and fragments shell from the brick surfaces into the molten slag, which speed up destruction of the bricks. When used in a petroleum coke gasifier, they will even cause more serious effects. Moreover, with its highest melting point being 2600° C., the element ZrO2 in the Cr2O3—Al2O3—ZrO2 material has no congruent melting point with the major content Cr2O3 except Al2O3. Thus, the product requires a higher firing temperature, which reduces the production rate and increases the cost. In addition, ZrO2 includes some activated elements, such as HfO2, which are harmful to human health.